1. Field of the Invention
The present invention relates to external prosthetics, and more specifically to a lock system for securing a prosthetic hard socket to a socket liner worn on a residual limb. The preferred lock system connects the distal end of the liner to the distal end of the hard socket, and the preferred embodiments are adapted to prevent air flow into or out of the hard socket through the lock mechanism during normal use of the prosthetic limb. This way, pressure in the distal end of the interior well of the hard socket may be effectively controlled by other mechanisms, such as a vacuum pump and/or other mechanisms. When a vacuum fit is desired, as discussed elsewhere in this document, the pressure inside the hard socket may be controlled and adjusted accurately and reliably because air is not leaking into the hard socket through the lock mechanism. The lock is actuated by a lever system at or near the outer surface of the hard socket, wherein the lever may be easily swung to open and close the lock. Alternative embodiments do not prevent air flow into or out of the hard socket during normal use of the prosthetic limb, but are lever-actuated.
When in the latched configuration, the preferred lock mechanism locks a liner pin into a bore in the hard socket, wherein the liner pin is an elongated pin assembly or other shaft that protrudes downward from the distal end of the liner on the wearer's residual leg. When the wearer unlatches the preferred lock mechanism, with an easy and comfortable swing of the latch handle, the liner pin, and therefore, the liner and residual limb, are removable from the socket.
2. Related Art
Optimum connection/suspension methods for securing a prosthetic limb to a residual limb take into account several factors, including control, comfort, ease of donning and removal, and long term effects on the health of the skin and other tissue. These factors are weighed differently and influenced differently, depending on the wearer's residual limb, level of activity, and preferences. One reason that suspension solutions are not simple is that gravitational and other forces tend to cause separation between a prosthetic limb and a residual limb. This happens especially during the swing phase of the gait, when a prosthetic leg is additionally subjected to centrifugal forces. Patients have routinely worn a variety of belts, straps, cuffs and harnesses to prevent the prosthetic limb from separating from the residual limb, but such devices are inconvenient and tend to cause chafing against the patient's body, giving rise to sores and abrasions. Advanced methods of suspension have been developed, for example “suction” and “vacuum” suspension, proximal attachment systems, and distal lock mechanisms. These modern methods are made more effective by modern roll-on liners that are adapted to grip the residual limb, and that are also adapted to attach/connect to the hard socket by said proximal attachment systems, distal lock mechanisms, and/or by suction or vacuum, relative to ambient air, inside the distal end of the well of the hard socket.
As discussed in more detail below, “suction” is typically used for systems that establish a pressure inside the distal end of the well of the hard socket that is moderately lower than ambient. Suction systems typically do not utilize any pump or other mechanical device to pump air out of the well of the hard socket; instead, for example, they utilize the force of the limb pressing into the socket, plus an air expulsion valve, to lower pressure inside the well. Therefore suction systems typically operate in the range of ½-4.9 psi (and preferably 1-1.5 psi) lower than ambient. “Vacuum” systems, on the other hand, utilize a vacuum pump or other mechanical device to remove air from the well, and may establish an air pressure inside the well in the range of 1-14.7 psi below ambient. More typically, however, vacuum systems operate in a well pressure range lower than suction systems, for example 5-14.7 psi below ambient.
In summary, therefore, a suction suspension is typically established and maintained by exhausting air from the distal end of the well when the user dons the socket and during each portion of the user's gait that works to push the limb deeper inside the hard socket. Vacuum, on the other hand, is typically established and maintained by use of a vacuum pump connected to the well of the hard socket.
It has long been appreciated that differential air pressure, referred by those of skill in the art as “suction” (or as “vacuum” when greater differentials are established), may be utilized to retain or suspend, or assist in retaining or suspending, a prosthetic limb on a patient's residual limb. “Suction” or “vacuum” suspension typically involves a hard socket and a cooperating liner positioned between the residual limb and the prosthetic socket. Many modern hard sockets are intended to fit accurately and snugly to the residual limb, and they are often “molded” to the shape of the limb. This fit tends to create a close fit between the outer surface of the liner and the inner surface of the hard socket, in effect, sealing or partially sealing the liner to said inner surface around the circumference of the residual limb along a significant length of the residual limb. Donning the hard socket, therefore, involves inserting the limb and liner into the socket and releasing pressure that builds in the distal end of the socket well because the air inside the socket does not easily escape past the liner and out of the socket. This release may be accomplished by a hand-operated or automatic valve, vacuum pump, and/or other pressure release/control means. Because of the close molded fit of many hard sockets to the residual limb of today's wearers, a “suction” or “vacuum” suspension is possible whether the wearer uses a “first generation” liner that has gel-like inner and outer surfaces, or a “second generation” liner that has a gel-like inner surface and a fabric outer surface, as further discussed below.
Socket liners frequently have been called “suction liners,” “gel liners,” “roll-on liners” or “suspension liners” and include the “first generation” of gel-layer-only liners, and also the modern “second generation” of multi-layer liners that include an outer layer of fabric and that currently are preferred by most wearers of prosthetics. Socket liners are usually fabricated from silicone, urethane, or other gel-like material that grips the limb to such an extent that they need to be rolled-onto the limb from a rolled-up “doughnut” form, rather than pulled on like a sock. When rolled-on, there is little, if any, air remaining between the inner surface of the roll-on liner and the limb, and the roll-on liner is snug against the limb all the way around the circumference of the limb. Also, the inner surface of the roll-on liner is of such material and tacky texture that air will not be able to, or be very unlikely to, enter between the roll-on liner and limb. Thus, the roll-on liner may be said to form a suction fit and/or a slight compression fit with the limb. A distal force on the liner, such as caused by the swing of a gait with a prosthetic leg, may tug on the roll-on liner but typically does not loosen, lower, or remove the liner from the limb. The liner is difficult to remove except by rolling the top edge of the liner down off of the limb. Thus, longitudinal (axial) forces on the liner do not easily pull the liner out of place or off of the limb. The liners are therefore quite effective in their adhering and staying on the residual limb, and many of the other features of modern suspension systems therefore focus on connection of the hard socket to the liner, as is discussed later in this document.
First generation liners, which featured a gel layer contacting both the residual limb (liner's inner surface) and also the socket (liner's outer surface), can be used to create a fairly high amount of pressure differential between the inside of the socket (in the “well” of the socket) and the surrounding ambient air. This could be accomplished by releasing air pressure from the distal end of the socket well, for example, by a manual valve in the socket wall, after which a very good seal between the limb and the liner and the liner and the hard socket could be maintained by the gel liner. Modern “second generation” liners, comprising a thin textile/fabric outer layer that is fixed to the gel-like inside layer, are similar to the first generation regarding the connection to the residual limb, but are different regarding the connection/cooperation with, the socket. Because the outer fabric layer of the second generation liners is not as tacky as a gel layer, these second generation liners do not seal as thoroughly as the first generation liners to the inner surface of the hard socket, resulting in less gripping of the socket by the liner and some small amount (albeit it slow) air flow between the liner and the socket interior surface. However, even with these second generation liners, a “partial suction” suspension is still possible, by using air expulsion valves, for example, and a “vacuum” suspension is still possible by using a vacuum pump.
Thus, second generation liners more accurately may be said to allow only “partial suction” (unless a vacuum pump is employed) because the fabric layer(s) do not form what would be called “true” or “pure” suction with the socket. The terms “suction liner” and “suction socket” are still used by many manufacturers, prosthetic technicians, insurance and medicare/medicaid entities, and wearers of prosthetics. See the discussion of suction liners in Janusson, et al. (U.S. Pat. No. 6,706,364) and Janusson, et al. (U.S. Pat. No. 6,626,952). The second generation liners, and the “partial suction” suspension they typically provide, are more comfortable for many wearers than a “true suction fit” that is more likely to be obtained by a gel liner without a fabric layer, wherein a gel-seal is formed by the liner both to the limb and to the socket. When a vacuum suspension is needed, the hard socket may be fit with a vacuum pump and control system.
The terms “suction,” “suction-fit,” and “suction suspension” herein refer to the general process known well in this field of providing a “roll-on” liner or other “interference” liner that helps keep a socket on a residual limb while creating at least a small amount of blockage/hindrance to air freely moving in and out of the socket well past the residual limb, wherein the air moving is typically due to the action of the limb in the socket. A “vacuum suspension” herein describes suspensions that utilize a vacuum pump or other active mechanical device to actively establish and maintain a lower air pressure in the distal end of the interior well of the hard socket, for example, a pressure that is preferably 5-14.7 psi less than ambient air pressure. In another approach, “suction”, “suction suspension” or “suction fit” may be defined as suspension/fittings that qualify under the medical code for “suction” and “vacuum”, “vacuum suspension” or “vacuum fit” may be defined as suspension/fittings that qualify under the medical code for “vacuum”.
Additional attachment systems may be used to supplement the suspension. One example is the distal lock of the instant inventors (Perkins, Coyote Design and Manufacturing, Inc.) in U.S. Pat. No. 6,334,876, issued Jan. 1, 2002, wherein a liner pin is locked into the distal end of the hard socket (see FIG. 4). In this Perkins device, a spring biases a plunger and an air-seal o-ring outward unless the wearer/assistant pushes the plunder radially inward. However, this Perkins device is not well-adapted for use with a vacuum system. If significant vacuum is established in the hard socket of this Perkins device, for example, with a vacuum pump, the vacuum will tend to pull the plunger and o-ring inward, thus undesirably unseating the o-ring and allowing air through the distal lock and into the socket.
Therefore, there is still a need for an improved distal lock system, especially for use in vacuum suspension systems. There is a need for such a distal lock system that does not break the vacuum established inside the hard socket, either during normal walking or during periods of sitting or resting. There is a need for such a distal lock system that is easy to use and that is reliable. There is a need for an improved lock actuation system that is easy and reliable to use with one hand or one finger, which may be used on a variety of prostheses including those for legs and arms, and which may be used in conjunction with vacuum, suction, or other attachment systems. The invention meets these needs.